1. Field of the Invention
This invention relates to improvements in flexible, resilient, polyurethane foams, and in particular to improvements in the characteristics of such foams when subjected to fire. Flexible resilient polyurethane foams are made by the reaction of polyols and organic polyisocyanates in the presence of a blowing agent and one or more catalysts. The foams find a variety of uses, such as carpet underlay, textile innerlining, mattresses, pillows, furniture padding, cushions, automobile crash pads, and insulation. Unless formulated with special additives, polyurethane foams burn readily when ignited. It is known in the art to add various flame retardant chemicals to polyurethanes foam forming reaction mixtures, in particular to add halogenated esters of phosphorus. This has resulted in some improvement in the flammability properties, the extent of burning after ignition being reduced and the foams may even be made self-extinguishing to some degree; but while combustion does occur the foam melts and drips flaming embers which may ignite other flammable materials in the vicinity and thus cause the fire to spread. In order to overcome this problem, other additives have been added to polyurethane foam-forming reaction mixtures to render the finished foams intumescent, or to produce a char, once they have been ignited. Such foams are less prone to the development of flaming, dripping, embers during combustion, and may produce a char which acts as a thermal insulation and thus aids in preventing the spread of a fire.
2. Description of the Prior Art
In U.S. Pat. No. 3,681,273 the use of a mixture of a nitrogen and phosphorus containing compound such as monoammonium phosphate, melamine phosphate, or urea phosphate, and an N-alkylol substituted polyalkylene polyamine as an additive to conventional flexible polyurethane foam reaction mixtures is disclosed. The resultant foams are flame-retardant, intumescent, and non-burning.
U.S. Pat. No. 3,803,063 discloses a flexible polyurethane foam reaction mixture containing an additive comprising a nitrogen and phosphorus containing compound such as monoammonium phosphate or an ammonium phosphate and a polycondensate of polymerized unsaturated fatty acids with aliphatic amines.
In U.S. Pat. No. 4,139,501, Rudner, Noone and Pauly disclose flexible polyurethane foams having reduced tendency to form burning embers when ignited and burned, produced by incorporating into the foam-forming reaction mixture a melamine derivative wherein one or more hydrogen atoms have been replaced by hydroxymethyl and/or lower alkoxymethyl groups. Alternatively, a halogenated phosphorus ester can also be included in the reaction mixture.